German Type IXB submarines were slightly larger than the original German Type IX submarines, later designated IXA. U-108 had a displacement of 1,051 tonnes (1,034 long tons) when at the surface and 1,178 tonnes (1,159 long tons) while submerged.[2] The U-boat had a total length of 76.50 m (251 ft), a pressure hull length of 58.75 m (192 ft 9 in), a beam of 6.76 m (22 ft 2 in), a height of 9.60 m (31 ft 6 in), and a draught of 4.70 m (15 ft 5 in). The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4,400 metric horsepower (3,240 kW; 4,340 shp) for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1,000 metric horsepower (740 kW; 990 shp) for use while submerged. She had two shafts and two 1.92 m (6 ft) propellers. The boat was capable of operating at depths of up to 230 metres (750 ft).[2]

The submarine had a maximum surface speed of 18.2 knots (33.7 km/h; 20.9 mph) and a maximum submerged speed of 7.3 knots (13.5 km/h; 8.4 mph).[2] When submerged, the boat could operate for 64 nautical miles (119 km; 74 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 12,000 nautical miles (22,000 km; 14,000 mi) at 10 knots (19 km/h; 12 mph). U-108 was fitted with six 53.3 cm (21 in) torpedo tubes (four fitted at the bow and two at the stern), 22 torpedoes, one 10.5 cm (4.13 in) SK C/32 naval gun, 180 rounds, and a 3.7 cm (1.5 in) as well as a 2 cm (0.79 in) anti-aircraft gun. The boat had a complement of forty-eight.[2]

The boat's first patrol began with her departure from Wilhelmshaven on 15 February 1941. She crossed the North Sea and entered the Atlantic via the gap between Iceland and the Faroe Islands, sinking Texelstroom on 22 February. She also sank Effna on the 28th; both ships met their end south of Iceland. She then docked at Lorient in occupied France on 12 March. She would be based there for most of the rest of her career.

Her second foray involved the sinking of HMS Rajputana, an armed merchant cruiser, west of Reykjavík on 13 April 1941. The Convoy Commodore, four officer and 35 ratings were lost.

U-108 sank Michael E., a CAM ship or 'Catapult Armed Merchantman', on the submarine's third patrol on 2 June 1941 in mid-Atlantic. She went on to sink Baron Nairn west of Cape Race (eastern Newfoundland and Labrador) on the 8th; the Greek ship Dirphys 600 nautical miles (1,100 km; 690 mi) east of Newfoundland, also on 8 July; Christian Krohg on the 10th; Ellinco on the 25th; Nicholas Pateras on the same day and Toronto on 1 July. The latter was a weather ship situated about 500 nmi (930 km; 580 mi) north of the Azores.

Patrol number four saw the boat covering the 'gap' between South America and Africa. She departed Lorient on 19 August 1941 and returned on 21 October.

She sank Cassequel, a neutral vessel, on 14 December 1941, 160 nmi (300 km; 180 mi) southwest of Cape St. Vincent, Portugal and Ruckinge (convoy HG 76) on the 19th, west of Lisbon as part of her fifth sortie.

The boat's sixth patrol, as part of Operation Drumbeat (Paukenschlag),[3] took her to the east coast of North America where she was again successful, sinking Ocean Venture on 8 February 1942, Tolosa on the 9th and Blink on the 12th. The U-boat had chased Blink, which had been hit by a non-detonating torpedo, the two vessels almost collided; which was only avoided by U-108 diving underneath the merchant ship.

She also sank Ramapo northwest of Bermuda on 16 February and Somme on the 18th.

The boat's seventh patrol was almost as successful as her sixth, sinking Modesta on 25 April 1942, Mobiloil on the 29th (which required a total of six torpedoes and many rounds from the 20mm and 37mm guns), Afoundria on 5 May, and Abgara a day later. On the return leg she encountered Norland on the 25th.

More success pennants were flown after her eighth patrol, which took her almost to the northern South American coast. She sank Tricula on 3 August 1942, Breňas on the 7th and Louisiana on the 17th.

The boat's ninth patrol was carried out in opposition to Operation Torch, (the Allied landings in North Africa). The submarine had not been off Morocco long before being attacked by a destroyer. The damage incurred was serious enough that the boat was obliged to return to France where effective repairs might be carried out.

The U-boat was attacked by a Catalina flying boat of 202 Squadron RAF on 10 February 1943 west of Morocco. The damage to the forward torpedo tubes forced her to return to Lorient.

In her last operational patrol, she departed Lorient on 1 April 1943. She was attacked by a destroyer on the 22nd but continued to shadow Convoy ON (S) 4 southeast of Greenland. She arrived at Stettin in modern-day Poland on 16 May. Bombed and sunk there 11 April, raised and decommissioned 17 July 1944. Scuttled there 24 April 1945.[4]

^Gannon, Michael - Operation Drumbeat - the dramatic true story of Germany's first U-boat attacks along the American coast in World War II, 1990, Harper and Row publishers, ISBN 0-06-016155-8, p. 202 .